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Pressuretrol

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bobbob
bobbob Member Posts: 70
I know many of you have heard discussions on this thousands of times, but I am new to this site, and just getting off the ground learning about my one-pipe, coal converted to NG system, so am still trying to get a grasp on some things...

1. What actually determines the steam pressure in a system? My system, as I have been observing it, very slowly reaches 3.2 ounces just about the time that the cycle is complete (as the thermostat shuts it down). Shut down seems to have nothing to do with what the Pressuretrol is set at (which is 1-1/2 lbs.)
2. It would seem logical to me that since water expands 1700 times when it becomes steam, then the diameter and length of all the pipes + the size and number of the radiators would dictate the pressure within the system once, of course, the vents have all closed. In other words, the steam creates its own pressure. Am I correct? Then it seems logical to me that if for some reason--a malfunction, or oversized boiler for examples-- my system would max out at or above what the pressuretrol is set at, then the pressuretrol would shut me down even if my thermostat is still calling for heat.
3. SO, it would seem logical to me that my system, since it is working as it is, could be considered to be well-balanced--no?

Sorry if I sound like Mr. Spock, but I suspect I may well have Vulcan genes...
ethicalpaul

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    I believe you understand it perfectly. You may just be lucky enough to have a well balanced and properly sized system.

    With any oil or gas fired coal conversion system, electricity is the control that makes the fire turn on and off. The thermostat is the switch that determines when the boiler needs to make steam and when to stop making steam. If the room temperature is lower than the thermostat point, the gas valve will open to make a fire that in turn makes the steam happen in the boiler. As the air is pushed out of the vents and the steam reaches the radiators, the room temperature increases and the thermostat electrical contacts open (or break) and the gas valve closes and the fire stops. The pressure in the system is a function of how large the flame is, and how big the pipes and radiators are. (how much space there is for the steam to fill).

    If your system is large enough, then the pressure never goes very high. If however the boiler is oversized or the pipes and radiators are not large enough to accommodate all that heat (or steam) then the pressure will increase to a point that the High Limit (a pressure control on the boiler itself) will be activated. Even though the thermostat is not yet satisfied, the burner will stop because the Pressure control opens a set of contacts to stop the electricity to the gas valve.

    There is at least one other control on you steam boiler called the Low Water Cutoff. (LWCO) If there is not enough water in the boiler to operate safely, (water level too low) then that control has switch contacts that can open to stop the gal from burning. So by design the LWCO, the High Limit Pressure control and the thermostat all need to be Closed to have a flame in the boiler. Since your pressure control never activates, consider yourself blessed to have a well designed system from the Dead Men that designed it years ago.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    ethicalpaul
  • mattmia2
    mattmia2 Member Posts: 9,840
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    What is missing here is the rate at which the surfaces of the radiators and other system components are absorbing and radiating the heat from the steam the steam and condensing it back in to water. If there is enough surface to do this as fast as the boiler produces steam then no pressure builds. If the boiler produces steam faster than the system can condense it back in to water then it builds pressure.
    EdTheHeaterManbburdethicalpaul
  • Jamie Hall
    Jamie Hall Member Posts: 23,544
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    This^^^. Or, to look at it another way, as soon as steam touches something cool, such as the inside of a radiator, it turns back into water and you lose that volume increase. So if things are going well, there never is more steam in the pipes and all than is needed to just barely fill them up.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • bobbob
    bobbob Member Posts: 70
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    Wow--then I guess I do have a pretty good grasp on things.
    I am wondering if my system was originally designed for OIL, not for coal--as I had assumed. When in history did we begin using oil in boiler systems? This house was built in 1900. I can't see any evidence that there was ever a coal chute, or coal bin or anything in this place. If burning oil and then converting to NG would require pretty much the same piping system, then that would make sense. SO, WAS OIL IN USE BY THE YEAR 1900?
    Thank you all for your inputs!
  • Jamie Hall
    Jamie Hall Member Posts: 23,544
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    1900 seems a bit early for oil. Much more likely that it was coal -- but equally likely that all evidence of a coal bin (and coal chute or window for it) has disappeared in some long forgotten renovations.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,090
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    Look for a replacement window that does not match the other basement windows.

    Also rub your hand on the sill plate on top of the walls. You will know when you find coal dust.

    Any little pulleys attached to the ceiling near the boiler?.....damper controls.
  • bburd
    bburd Member Posts: 926
    edited March 2022
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    Basements in coal heated houses get pretty dirty. When my 1927 house in Pennsylvania was converted from coal to oil in 1947, the ceilings were sprayed white— probably to cover the soot and coal dust. There were filled holes in the floor slab opposite the boiler where the coal bin wall studs were removed. I could also see where those same studs were nailed to the floor joists above.

    Bburd
  • ethicalpaul
    ethicalpaul Member Posts: 5,757
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    My house in NJ about 12 miles west of NYC built in 1913 had a coal bin in the blueprints and no sign of coal today
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el